Synergistic effect on co-pyrolysis of capsicum stalks and coal

With the depletion of fossil fuel and the concern about environmental issues, the utilization of biomass resources has attracted increasing worldwide interest. The pyrolysis behavior of capsicum stalks and Baoji coal mixtures was investigated by TG-DSC. Results show that the thermal degradation temperature range of capsicum stalks was 290 to 387°C, while that of Baoji coal was 416 to 586°C. According to the comparison of experimental values and calculation results based on the algebraic sum of the fraction of individual mixture samples, the synergistic effect was significant at temperature ranges of 314 to 369 and 431 to 578°C. The synergistic effect could also be seen from the kinetic studies performed according to the Fried man Method. The rate of mass loss and k in the experiment is higher than the calculated values in the range of 314 to 368°C and that in the experiment is lower than the calculated values in the range of 431 to 578°C. Meanwhile, it was indicated that the pyrolysis process of capsicum stalks, Baoji coal and their mixtures could be described by one, two and four first order reactions, respectively.Keywords: Pyrolysis, capsicum stalks, mixing rate, kinetics, synergistic effec

Progress in low carbon technologies for large-scale coal-fired power plants

China’s total carbon emissions are approximately 11 billion tons, with around 40% of CO2 being produced by the coal-fired power plants (CFPP). Therefore, reducing carbon emissions from the CFPP is critical in achieving the Dual-Carbon target. This paper focused on the advancements in the low-carbon/carbon-neutral fuel substitution technologies (such as biomass, sludge, hydrogen/ammonia, etc.) and the CCUS (carbon capture, utilization and storage). The CFPP coupled with biomass includes direct and indirect coupling, but are subject to the supply and price of biomass feedstock. To address these challenges, a comprehensive “planting-harvesting-transportation-storage-pretreatment-combustion” approach was recommended to ensure an effective control throughout the entire chain. Initial pilot test on a 660 MW CFPP revealed a substantial reduction in CO2 emissions by 772500 tons annually. The high-water content of municipal sludge, reaching up to 80%, necessitates drying prior to entering the boiler. Current steam drying and flue gas drying technologies entail substantial investment and operational costs, with the dried sludge still retaining high water content and associated problems such as odor. Consequently, the blending ratio in the CFPP remains below 8%. A sludge carbonization technology based on a biomass heat source can address these challenges, which allows for the direct production of odorless sludge char in sewage plants with a calorific value of about 10.26 MJ/kg. This technology enables an increased blending ratio in the CFPP to 20%−30%, thereby significantly reducing coal consumption and CO2 emissions. The blending of hydrogen/ammonia necessitates addressing the issues of ammonia escape and NOx emission under high blending ratios. Experiments for co-firing of coal and ammonia were conducted on 300 MW and 600 MW CFPP in China to address the challenges of ammonia escape and NOx emissions under high blending ratios. The results showed that combustion control can achieve a higher NH3 burn-up rate with a slight increase in NOx emissions. However, the commercialization of hydrogen/ammonia blending in the CFPP is constrained by the cost of hydrogen and ammonia. The commercialization of pre-combustion decarbonization technology, such as IGCC, faces significant limitations due to high costs. Several foreign demonstration projects were discontinued. The construction costs and equipment reliability are crucial for promoting the commercialization of this technology. Carbon capture technologies in combustion processes include oxygen-enriched combustion and chemical chain combustion. The power generation efficiency of atmospheric oxyfuel combustion is lower by 8%−12% compared to air combustion due to the energy consumption associated with air separation and recycling processes. Transitioning from atmospheric oxyfuel combustion to pressurized oxyfuel combustion can further increase the net power generation efficiency. Notably, China has constructed the world’s largest 4 MW chemical-looping combustion (LCL) demonstration plant. The LCL also has a potential application in the gasification industry. Post-combustion carbon capture predominantly employs the solution absorption technology, while the solid adsorption technology offers a lower regeneration energy consumption. However, some challenges remain in reducing energy consumption and costs to facilitate the large-scale commercialization of this technology

Experimental study on preheating combustion characteristics and NOx emission of pulverized coal based on an entrained-flow gasifier

Pulverized coal preheating combustion technology has been proven to be a clean and efficient combustion technology. In view of the limited space and load-bearing capacity around the large coal-fired boiler, a novel technology and system with a compact entrained-flow gasifier to preheat pulverized coal is proposed for the first time. The preheating characteristics in the gasifier and the combustion characteristics of the preheated fuel in the down-fire combustor (DFC) are studied on the novel self-built preheating combustion test rig. The migration and transformation of coal nitrogen during the preheating combustion are investigated. The results show that the experiment system can operate continuously and steadily with small fluctuations in pressure and temperature. The temperature gradient in the gasifier is large, and the high temperature zone is located near the burner plane. The maximum temperature can reach 1 115 ℃, while the outlet temperature of the gasifier decreases to 850 ℃. The high temperature coal gas and char produced by the entrained-flow gasifier are provided to the DFC continuously and steadily. The volume fractions (dry basis) of CO, H2 and CH4 in high temperature coal gas are 13.15%, 8.72% and 0.78%, respectively. Compared to the raw coal, the size of the preheated char decreases. The 50% cut particle size of raw coal is 43 μm, while the preheated semi-coke is 24 μm. The specific surface area increases from 4.05 m2/g to 216.44 m2/g after preheating. At the same time, the pore volume of the char particles increases, and the combustion characteristics are improved. During the preheating process, 96.33% of volatile matter and 40.23% of fixed carbon are released into high temperature coal gas. Also, 69.74% of coal nitrogen is transformed in the gas phase, and 47.67% is converted into N2, the rest into NH3 and HCN. Stable combustion could be achieved with preheated fuels in the DFC with no ignition delay and a uniform temperature distribution. Most of the NH3 and HCN and the nitrogen released from char are converted into N2 in the main combustion zone. There is no NO generation in the main combustion zone. The CO and NOx emissions at the outlet of the DFC are 8.17 mg/Nm3 (6% O2) and 143.02 mg/Nm3 (6% O2), respectively. The combustion efficiency is 99.75%. After the pulverized coal is preheated by the new entrained-flow gasifier and burn in the DFC, only 4.69% of coal N is converted into NO

Short Review on the Origin and Countermeasure of Biomass Slagging in Grate Furnace

Given the increasing demand for energy consumption, biomass has been more and more important as a new type of clean renewable energy source. Biomass direct firing is the most mature and promising utilization method to date, while it allows a timely solution to slagging problems. Alkali metal elements in the biomass fuel and the ash fusion behavior, as the two major origins contributing to slagging during biomass combustion, are analyzed in this paper. The slag presents various layered structures affected by the different compositions of ash particles. Besides, the high-temperature molten material which provides a supporting effect on the skeletal structure in biomass ash was proposed to evaluate the ash fusion characteristics. In addition, numerous solutions to biomass slagging, such as additives, fuel pretreatment and biomass co-firing, were also discussed

Water Wall Tubes’ High Temperature Corrosion Root Cause Investigation: A 300 MW Level Boiler Case

High temperature corrosion poses a great threat to boiler water wall safe operation. To investigate the corrosion root cause, a 300 MW level boiler water wall high temperature H2S corrosion case was reported. The typical hydrogen sulfide H2S corrosion feature was large amounts of sulfur which could be found in the cut down sample tube corrosion layer, with a thickness of 482 μm. In addition, huge amounts of lead (Pb) could be found in the corrosion layer, which resulted from the lead sulfide (PbS) deposition when the high temperature flue gas condensed at the water wall tubes. Meanwhile, the sulfur in the corrosion layer was closely related to the H2S concentration in the water wall ambience. The related ambience test showed that the H2S could achieve up to 1000 ppm when the boiler was in operation, far larger than the suggested reference value of 100 ppm. Hence, the overlarge H2S concentration was a vital factor for the tube corrosion. To further investigate the reason why the H2S was kept in such high concentration in the boiler long term operation, and the reasons for the over-high sulfur content in the coal and the over-large diameter of the imaginary circle of primary air (DICPA), two factors were obtained. The peak sulfur content reached 2.5% and the suggested sulfur content was below 1%. The DICPA was so large (1580 mm) that the pulverized coal easily scoured the water wall tubes, which would boost the thinning process of the tubes. To relieve the high temperature corrosion, improve the coal qualities, decrease the DICPA, adjust the operation diameter and adopt a coating technology four measures were suggested

Water Wall Tubes’ High Temperature Corrosion Root Cause Investigation: A 300 MW Level Boiler Case

High temperature corrosion poses a great threat to boiler water wall safe operation. To investigate the corrosion root cause, a 300 MW level boiler water wall high temperature H2S corrosion case was reported. The typical hydrogen sulfide H2S corrosion feature was large amounts of sulfur which could be found in the cut down sample tube corrosion layer, with a thickness of 482 μm. In addition, huge amounts of lead (Pb) could be found in the corrosion layer, which resulted from the lead sulfide (PbS) deposition when the high temperature flue gas condensed at the water wall tubes. Meanwhile, the sulfur in the corrosion layer was closely related to the H2S concentration in the water wall ambience. The related ambience test showed that the H2S could achieve up to 1000 ppm when the boiler was in operation, far larger than the suggested reference value of 100 ppm. Hence, the overlarge H2S concentration was a vital factor for the tube corrosion. To further investigate the reason why the H2S was kept in such high concentration in the boiler long term operation, and the reasons for the over-high sulfur content in the coal and the over-large diameter of the imaginary circle of primary air (DICPA), two factors were obtained. The peak sulfur content reached 2.5% and the suggested sulfur content was below 1%. The DICPA was so large (1580 mm) that the pulverized coal easily scoured the water wall tubes, which would boost the thinning process of the tubes. To relieve the high temperature corrosion, improve the coal qualities, decrease the DICPA, adjust the operation diameter and adopt a coating technology four measures were suggested